Hydraulic shock absorbers have long been in widespread use for applications requiring the absorption of kinetic energy of a moving part. Such hydraulic shock absorbers employ the forcing of a hydraulic fluid through a resistance flow passage defining a resistance to fluid flow, with the energy dissipated through the movement of fluid through the restrictive passage.
This general arrangement has been refined in many ways in order to optimize the basic effect. One such refinement involves the use of orifices or knife edge flow in order to establish the resistance to hydraulic flow. Commonly, a piston is moved in a cylinder to force the hydraulic fluid through a relatively small diameter orifice such that fluid flow therethrough is turbulent. Turbulent flow dissipates energy much more effectively than does laminar flow.
In addition, the resistance to laminar flow is primarily a function of the viscosity of the hydraulic fluid, which viscosity will typically vary greatly with temperature.
Thus, the shock absorber will have greatly differing operating characteristics if laminar flow constitutes a substantial proportion of the resistance to movement of the parts connected to the elements through which the force is dissipated.
Another such design refinement includes the provision of a series of orifices, in the case of a piston and cylinder, in which the flow restriction increases as the piston approaches the end of its stroke. This is in order to achieve more or less deceleration force as the velocity of the piston increases. That is, at initial impact, the velocity of the relatively moving parts is generally much higher than as the piston approaches the end of its stroke. Since the resistance to flow is much higher at higher velocities due to viscous damping forces, a greater effective orifice is provided at the initial portion of the piston stroke in order to offset the effects of velocity and to produce a constant or linear net decelerating force acting on the connected parts.
In order to provide a variable range characteristic to such shock absorbers, it has heretofore been proposed, and shock absorbers have been designed, in which a variable orifice has been provided by providing a coacting sleeve which when rotated produces a variable area of each of the orifices in the series.
The prior art approach in general provided adjustment in such a manner that the flow through the grooves was upstream of the orifice restriction such as to pressurize the grooves at a relatively high pressure forcing the hydraulic fluid between the metering sleeve or tube and the surrounding cylinder. The flow between this clearance space being primarily laminar results in a substantial proportion of the hydraulic resistance being laminar flow, producing the aforementioned difficulties with regard to changing characteristics with varying temperature conditions.
In U.S. Pat. No. 4,059,175 of the present inventors, an improvement over this general arrangement is disclosed in which such high pressure groove condition is precluded. This was achieved by providing a groove formed on the sleeve interior having one side which was inclined at an angle to the axis of the cylinder. With the provision of a series of holes or ports in the piston, a variable area orifice was thus provided, depending on the rotational position of the surrounding sleeve due to a differing overlying area of the cylinder ports and the tube.
In this arrangement, the groove area downstream of the orifice formed by the overlying cylinder ports and groove are selected to be always greater than the area of the overlying groove at this particular position of the cylinder and sleeve.
This produces the advantageous result of a low pressure condition in the groove and virtually the entire hydraulic resistance is defined by the orifices. Thus, turbulent flow constituted the entire hydraulic resistance through the shock absorbers since leakage between the cylinders and sleeve was thereby eliminated.
The groove configuration in this patent is produced by the variable depth interception with the sleeve interior of a lathe tool having an inclined shoulder thereon such as to produce one edge of the groove which shifts axially in various rotative positions about the cylinder axis to produce the metering action by relative rotation of the sleeve over the cylinder ports.
While producing the aforementioned advantages, the cross sectional area of the groove necessarily declines as the orifice area declines.
While, as described therein, the groove area is always maintained to be greater than the cross sectional area of the orifice, nonetheless the larger the groove area, the less resistance to flow resulting in such lower pressure in the groove.
Thus, it would be advantageous if the groove area did not decline at any point of adjustment in the orifice sizes.
Furthermore, the flow down through the groove to the exhaust opening is essentially in a single direction, due to the groove geometry. It would further reduce the groove pressure if two directional flow could be achieved.
The particular machining process also requires control over the in-and-out depth of the cut of the tool as well as the geometry of the tool introducing two different factors which must be controlled to produce the required geometry of the groove.
It would of course be advantageous if the number of the geometry influencing factors in the machining process could be reduced while still providing a relatively low cost machining technique.
The metering grooves according to U.S. Pat. No. 4,059,175 also are of a variable width with the shallow ramped side producing the variation in width which in turn provides the variable area orifice, as the metering sleeve is rotated over the cylinder. This configuration particularly at the smaller area adjustment tends to reduce the knife edge configuration of the orifice formed by the overlay of the cylinder ports and the metering grooves.
It would be preferable for the groove side surface to not be adjacent the ports so as to maximize the knife edge configuration and the turbulence of the flow from the cylinder port into the metering groove.
Another advantage of the aforementioned patented shock absorber is the range of adjustment. Most such arrangements in the past allowed less than 90.degree. of adjustment, whereas, in the design described in U.S. Pat. No. 4,059,175, a 180.degree. adjustment range is possible. This enables rotation in either direction to provide such 180.degree. adjustment. The increased range of course provides a more precisely controlled tailoring of the shock absorber characteristic and to a wider range of load applications.
It would of course be desirable to maintain or increase such range of adjustment while simplifying the groove machining techniques as well as maintaining maximum groove cross sectional area.
It would also be advantageous if such range could be increased beyond 180.degree. to further enhance the capability of the shock absorber to varying load applications.
In this patent, there is also described the use of a single spiral groove which registers with the cylinder holes. While relatively simple to manufacture by thread forming or machining techniques, this relatively constrains the cylinder hole configuration which may be placed in phase with a constant pitch helix.
It is desirable to enable the cylinder holes to be placed to programmed locations in order to produce the linearizing of the decelerating force, and such spiral groove configuration inhibits the design control over the location of the cylinder ports.
Accordingly, it is an object of the present invention to provide a hydraulic shock absorber of the type including a piston displaceable within a cylinder forcing fluid through a series of orifices defined by the overlaying of a corresponding series of grooves formed on the inner diameter of the metering sleeve in which the groove configuration and the relationship of the orifices is such as to insure substantially the entire hydraulic resistance of the shock absorbers defined by turbulent flow through the orifices so formed.
It is another object of the present invention to provide such a shock absorber in which the groove cross sectional area is maintained at a maximum throughout the adjustment range defined by the variation in the orifice cross sectional area achieved by rotation of the overlying metering sleeve on the cylinder.
It is a further object of the present invention to provide such shock absorbers in which the groove configuration may be readily machined by relatively simple machining techniques and in which the groove geometry is relatively easily controlled during the machining process.
It is yet another object of the present invention to provide such a shock absorber in which a 180.degree. and greater change of adjustment is provided.
It is still another object of the present invention to provide an orifice geometry which achieves maximized turbulent flow by a knife edge geometry.